Tens of thousands of workers have taken to the streets of European cities to protest at job cuts, public spending reductions and tax rises.

Waves of demonstrators marched through Brussels toward European Union buildings, aiming to reinforce the impact of Spain's first nationwide strike in eight years.

Unions estimated the turnout in Brussels at 100,000 people. Some protesters there confronted riot squads with a sit-down protest in the middle of the street. About 150 people were detained, some in scuffles with police.

Strikes or protests took place in Greece, Portugal, Ireland, Slovenia and Lithuania, all aimed at the austerity plans that European governments have implemented to try to control their debt.

The march in Brussels came as the EU Commission proposed new penalties to punish member states that have run up deficits.

The proposal, backed by Germany, was running into strong opposition from France, which wants elected politicians, not rigid accounting rules, to decide on what sanctions big spending countries should face.

"It is a bizarre time for the European Commission to be proposing a regime of punishment," said John Monks, general secretary of the European Trade Union Confederation. "How is that going to make the situation better? It is going to make it worse."

Unions fear workers will become the biggest victims of an economic crisis set off by bankers and traders, many of whom were rescued by massive government intervention.

"There is a great danger that the workers are going to be paying the price for the reckless speculation that took place in financial markets," Monks said. "You really got to reschedule these debts so that they are not a huge burden on the next few years and cause Europe to plunge down into recession."

The strike in Spain was the country's first general strike since 2002 and marked a break in the once-close relationship between unions and the Socialist government.